/* ----------------------------------------------------------------------
* Copyright (C) 2011 ARM Limited. All rights reserved.
*
* $Date:        15. February 2012
* $Revision: 	V1.1.0
*
* Project:      CMSIS DSP Library
* Title:		arm_sqrt_q15.c
*
* Description:	Q15 square root function.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Version 1.1.0 2012/02/15
*    Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.0 2011/03/08
*     Alpha release.
*
* Version 1.0.1 2011/09/30
*     Beta release.
*
* -------------------------------------------------------------------- */
#include "arm_math.h"
#include "arm_common_tables.h"


/**
 * @ingroup groupFastMath
 */

/**
 * @addtogroup SQRT
 * @{
 */

/**
 * @brief  Q15 square root function.
 * @param[in]   in     input value.  The range of the input value is [0 +1) or 0x0000 to 0x7FFF.
 * @param[out]  *pOut  square root of input value.
 * @return The function returns ARM_MATH_SUCCESS if input value is positive value or ARM_MATH_ARGUMENT_ERROR if
 * <code>in</code> is negative value and returns zero output for negative values.
 */

arm_status arm_sqrt_q15(
    q15_t in,
    q15_t* pOut)
{
	q15_t number, temp1, var1, signBits1, half;
	q31_t bits_val1;
	float32_t temp_float1;

	number = in;

	/* If the input is a positive number then compute the signBits. */
	if(number > 0) {
		signBits1 = __CLZ(number) - 17;

		/* Shift by the number of signBits1 */
		if((signBits1 % 2) == 0) {
			number = number << signBits1;
		} else {
			number = number << (signBits1 - 1);
		}

		/* Calculate half value of the number */
		half = number >> 1;
		/* Store the number for later use */
		temp1 = number;

		/*Convert to float */
		temp_float1 = number * 3.051757812500000e-005f;
		/*Store as integer */
		bits_val1 = *(int*) &temp_float1;
		/* Subtract the shifted value from the magic number to give intial guess */
		bits_val1 = 0x5f3759df - (bits_val1 >> 1);  // gives initial guess
		/* Store as float */
		temp_float1 = *(float*) &bits_val1;
		/* Convert to integer format */
		var1 = (q31_t)(temp_float1 * 16384);

		/* 1st iteration */
		var1 = ((q15_t)((q31_t) var1 * (0x3000 -
		                                ((q15_t)
		                                 ((((q15_t)
		                                    (((q31_t) var1 * var1) >> 15)) *
		                                   (q31_t) half) >> 15))) >> 15)) << 2;
		/* 2nd iteration */
		var1 = ((q15_t)((q31_t) var1 * (0x3000 -
		                                ((q15_t)
		                                 ((((q15_t)
		                                    (((q31_t) var1 * var1) >> 15)) *
		                                   (q31_t) half) >> 15))) >> 15)) << 2;
		/* 3rd iteration */
		var1 = ((q15_t)((q31_t) var1 * (0x3000 -
		                                ((q15_t)
		                                 ((((q15_t)
		                                    (((q31_t) var1 * var1) >> 15)) *
		                                   (q31_t) half) >> 15))) >> 15)) << 2;

		/* Multiply the inverse square root with the original value */
		var1 = ((q15_t)(((q31_t) temp1 * var1) >> 15)) << 1;

		/* Shift the output down accordingly */
		if((signBits1 % 2) == 0) {
			var1 = var1 >> (signBits1 / 2);
		} else {
			var1 = var1 >> ((signBits1 - 1) / 2);
		}

		*pOut = var1;

		return (ARM_MATH_SUCCESS);
	}
	/* If the number is a negative number then store zero as its square root value */
	else {
		*pOut = 0;
		return (ARM_MATH_ARGUMENT_ERROR);
	}
}

/**
 * @} end of SQRT group
 */
